Antigen binding formats for use in therapeutic treatments or diagnostic assays

ABSTRACT

The present invention relates to antigen binding formats for use in therapeutic treatments or diagnostic assays. The present invention relates to an antigen-binding format consisting of: —a first fusion protein wherein the CH1 constant domain of an antibody is fused i) by its N-terminal end to the C-terminal end of a variable domain of an antibody and ii) by its C-terminal end to the N-terminal end of a variable domain of an antibody and, —a second fusion protein wherein the CL constant domain of an antibody is fused by its N-terminal end to the C-terminal end of a variable domain of an antibody.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is divisional application of U.S. patent application Ser. No. 13/976,481 filed Jun. 27, 2013, and that application was a Rule 371 national stage filing from PCT/EP2011/074241 filed Dec. 29, 2011, which claimed priority to U.S. Provisional Application 61/428,294 filed Dec. 30, 2010 and European Application 10306541.3 filed Dec. 30, 2010.

FIELD OF THE INVENTION

The present invention relates to antigen binding formats for use in therapeutic treatments or diagnostic assays.

BACKGROUND OF THE INVENTION

Therapeutic monoclonal antibodies (mAbs) have met some successes in the clinic over the last years, particularly in oncology. More than twenty five mAbs are on the market.

Many technical efforts have been made to generate second generation mAbs with decreased immunogenicity and with optimized effector functions. Since the majority of therapeutic antibodies are IgG1, at least part of the observed in vivo effects of mAbs might be induced following interactions between their Fc region and FcγR. Notably, the ability of mAbs to kill tumor cells has been related to their capacity to recruit and activate effector cells such as NK cells and macrophages through receptors for the Fc portion of IgG (FcγR).

However, recent reports have shown that the efficiency of IgG1 human therapeutic mAbs is strongly affected by various parameters: changes in Fc glycosylation, FcγRIIIA polymorphism, interaction with inhibitory FcγRIIB, and competition with endogenous IgG for FcγRI and FcγRIII binding. For instance, studies with FcγR−/− mice have revealed the implication of different FcγR in some in vivo mechanisms of action of two widely used therapeutic mAbs, trastuzumab and rituximab. These cytotoxic mAbs directed against tumors engage both activating (FcγRIIIA) and inhibitory (FcγRIIB) receptors. In these studies, a more pronounced tumor regression was observed in FcγRIIB-deficient mice than in wild-type mice, whereas FcγRIIIA-deficient mice were unable to stop tumor growth in the presence of therapeutic mAbs. In humans, a recent study has shown that the therapeutic efficiency of rituximab (a chimeric human IgG1) in patients with non-Hodgkin lymphoma is partly correlated with FcγRIIIA polymorphism. Thus, patients homozygous for the Val158 allele (IgG1 high binder) exhibited a higher response to the treatment than the patients homozygous for the Phe158 allele (IgG1 low binder). Similarly, engineered IgG glycoforms have been shown to trigger optimized ADCC through the recruitment of FcγRIIIA. A first study showed that an IgG1 antibody engineered to contain increasing amounts of bisected complex oligosaccharides (bisecting N-acetylglucosamine, GlcNAC) allows the triggering of a strong ADCC as compared to its parental counterpart. Second, a lack of fucose or low fucose content on human IgG1 N-linked oligosaccharides has been shown to improve FcγRIIIA binding and ADCC as well as to increase the clearance rate of Rhesus D+ red blood cells in human volunteers. Moreover, it has been recently shown that the antigenic density required to induce an efficient ADCC is lower when the IgG has a low content in fucose as compared to a highly fucosylated IgG.

The idea that a better control of Fc/FcγR interactions was needed when using therapeutic mAbs has been clearly argued in the early 80's and led to the concept and the generation of bispecific antibodies (bsAbs), using biochemical approaches and then molecular engineering in the early 90's. Bispecific antibodies, able to bring together target cells and activated effector cells have important potential advantages over whole naked mAbs. Notably, with regard to NK cells recruitment and activation, bsAbs make it possible to overcome most of the problems encountered with therapeutic mAbs. First, it is far easier to use an antibody arm binding to FcγRIIIA than to engineer and fine-tune the interaction between the antibody Fc region and FcγRIIIA. It is indeed possible to select a FcγRIIIA binder devoid of cross reaction for inhibitory FcγRIIB and targeting an epitope not involved in the Fc binding to avoid the high/low binder FcγRIIIA polymorphism issue, as well as endogenous IgG competition. Moreover, antibody fragments are not concerned by glycosylation issues, and it is possible to fine-tune the affinity of the antibody from a μM to a nM range, i.e., an affinity up to 1,000 fold higher than that involved in Fc/FcγRIIIA interaction. Thus, a number of attempts have been made to create anti-FcγRIIIA×anti-target bsAbs.

However, for years, these attempts were hindered by the impossibility to efficiently produce such molecules, the most efficient techniques requiring grams of mAbs to produce milligrams of heterogeneous preparations of bsAbs. Therefore, the first generation of bsAbs never reached the market, mostly due to the cost of getting molecules with bi-functional properties in large amounts for a therapeutic use.

The inventors have recently developed a new generation of bispecific antibodies, based on llama VHH (sdAb for single domain antibody or also Nb for nanobody), that can be easily produced in E. coli and that overcome the limitations listed above, while being able to exert a strong tumor lysis at extremely low concentrations. These bispecific antibodies are described in the International Patent Application no WO/2006/064136. This generation of therapeutic antibodies has the potential to rapidly translate into efficient therapeutics. Although these bsAbs accumulate within the tumor, they suffer from a rapid elimination due to their relatively small size, below the renal threshold (around 60 kDa), and to the absence of Fc region involved in the interaction with the FcRn receptor, responsible for the long serum half-life of full length IgG. Thus, there is a need to improve these bsAbs in terms of efficiency, serum half-life and biodistribution.

SUMMARY OF THE INVENTION

The present invention relates to an antigen-binding format consisting of:

-   -   a first fusion protein wherein the CH1 constant domain of an         antibody is fused i) by its N-terminal end to the C-terminal end         of a first variable domain of an antibody and ii) by its         C-terminal end to the N-terminal end of a second variable domain         of an antibody and,     -   a second fusion protein wherein the CL constant domain of an         antibody is fused by its N-terminal end to the C-terminal end of         a third variable domain of an antibody.

DETAILED DESCRIPTION OF THE INVENTION

The inventors have now created new antigen binding formats to increase the serum half-life of the original bsAb format (54 kDa) described in the International Patent Application WO/2006/064136 by fusing one additional sdAb (single domain antibody) to the C-terminal end of the CH1 domain of the Cκ/CH1 heterodimerization motif (FIG. 1). They have surprisingly shown that said fusion allows the production of various functional antigen binding formats differing in size and valence for the targeted antigens. The fact that sdAbs fused via their N-terminal domain to the C-terminal domain of CH1 remain active is remarkable because this N-terminal end is located at the vicinity of the antigen binding site. Major steric hindrance between the antigen and the heterodimerization motif might have occurred. However the inventors demonstrated that functional antigen binding formats may be obtained.

Antigen-Binding Formats of the Invention

Accordingly, the present invention relates to an antigen-binding format consisting of:

-   -   a first fusion protein wherein the CH1 constant domain of an         antibody is fused i) by its N-terminal end to the C-terminal end         of a variable domain of an antibody and ii) by its C-terminal         end to the N-terminal end of a variable domain of an antibody         and,     -   a second fusion protein wherein the CL constant domain of an         antibody is fused by its N-terminal end to the C-terminal end of         a variable domain of an antibody.

According to the invention, the antigen binding format of the invention represents a heterodimeric format that reproduces the CL/CH1 heterodimerization motif of a classic antibody and thus allows the correct folding of the antigen binding formats of the invention in a cellular context. According to the invention, the CH1 constant domain of the first fusion protein and the CL constant domain of the second fusion protein are therefore linked together via a disulfide bond.

According to the present invention, “antibody” or “immunoglobulin” have the same meaning, and will be used equally in the present invention. In natural antibodies, the two heavy chains are linked to each other by disulfide bonds and each heavy chain is linked to a light chain by a disulfide bond. There are two types of light chain, lambda (λ) and kappa (κ). There are five main heavy chain classes (or isotypes) which determine the functional activity of an antibody molecule: IgM, IgD, IgG, IgA and IgE. Each chain contains distinct sequence domains. The light chain includes two domains, a variable domain (VL) and a constant domain (CL). The heavy chain includes four domains, a variable domain (VH) and three constant domains (CH1, CH2 and CH3, collectively referred to as CH). The variable regions of both light (VL) and heavy (VH) chains determine binding recognition and specificity to the antigen. The constant region domains of the light (CL) and heavy (CH) chains confer important biological properties such as antibody chain association, secretion, transplacental mobility, complement binding, and binding to Fc receptors. The Fv fragment is the N-terminal part of the Fab fragment of an immunoglobulin consisting of the variable domains of one light chain and one heavy chain. The specificity of the antibody resides in the structural complementarity between the antibody combining site and the antigenic determinant. Antibody combining sites are made up of residues that are primarily from the hypervariable or complementarity determining regions (CDRs). Occasionally, residues from nonhypervariable or framework regions (FR) influence the overall domain structure and hence the combining site. The CDR refers to amino acid sequences which together define the binding affinity and specificity of the natural Fv region of a native immunoglobulin binding site. The light and heavy chain variable domains of an immunoglobulin have three CDRs, designated L-CDR1, L-CDR2, L-CDR3 and H-CDR1, H-CDR2, H-CDR3, respectively. An antigen-binding site, therefore, includes six CDRs, comprising the CDR set from each of a heavy and a light chain V region. FR refers to amino acid sequences interposed between CDRs.

The term “monoclonal antibody” or “mAb” as used herein refers to an antibody molecule of a single amino acid composition, that is directed against a specific antigen and that is produced by a single clone of B cells or hybridoma. Accordingly, the term “hybridoma” denotes a cell, which is obtained by subjecting a B cell prepared by immunizing an animal with an antigen to cell fusion with a myeloma cell derived from a mouse or the like which produces a desired monoclonal antibody having an antigen specificity.

In a particular embodiment, the CH1 and CL constant domains of the invention are humanized constant domains, and more preferably full-human CH1 and CL constant domains.

By “humanized”, it is meant mutated so that immunogenicity upon administration in human patients is minor or nonexistent. Humanizing an antibody (e.g. a murine or Camelid antibody), according to the present invention, comprises a step of replacing one or more of the amino acids of said antibody by their human counterpart as found in the human consensus sequence, without that antibody losing its typical character, i. e. the humanization does not significantly affect the antigen binding capacity of the resulting antibody.

In a particular embodiment, the CL domain is from a lambda (λ) or a kappa (κ) light chain.

In a particular embodiment, the CH1 domain is from an IgG, such as IgG1, IgG2, IgG3, or IgG4. Alternatively, the CH1 domain is from an IgA, IgD, IgE or IgM.

In a particular embodiment, the variable domain is selected from the group consisting of VH domains, VL domains, or single domain antibodies (sdAbs).

The term “single domain antibody” (sdAb) or “VHH” refers to the single heavy chain variable domain of antibodies of the type that can be found in Camelid mammals which are naturally devoid of light chains. Such VHH are also called “Nanobody®”. According to the invention, sdAb can particularly be llama sdAb.

In a particular embodiment, the single domain antibody (VHH) domain is humanized.

In a particular embodiment, the variable domain is a VH domain or a single domain antibody (sdAb).

In a particular embodiment, the VH domain is a humanized VH domain, and more preferably a fully human VH domain.

Typically, the variable domain may be directed against any antigen.

For example, the variable domain may be specific for an immune cell regulatory molecule such as CD3, CD4, CD8, CD25, CD28, CD26, CTLA-4, ICOS, or CD11a. Other suitable antigens include but are not limited to those associated with immune cells including T cell-associated molecules, such as TCR/CD3 or CD2; NK cell-associated targets such as NKG2D, FcγRIIIa (CD16), CD38, CD44, CD56, or CD69; granulocyte-associated targets such as FcγRI (CD64), FcαRI (CD89), and CR3 (CD11b/CD18); monocyte/macrophage-associated targets (such as FcγRI (CD64), FcαRI (CD89), CD3 (CD11b/CD18), or mannose receptor; dendritic cell-associated targets such as FcγRI (CD64) or mannose receptor; and erythrocyte-associated targets such as CRI (CD35).

Alternatively, the variable domain according to the invention may be directed against a cancer antigen. Known cancer antigens include, without limitation, c-erbB-2 (erbB-2 is also known as c-neu or HER-2), which is particularly associated with breast, ovarian, and colon tumor cells, as well as neuroblastoma, lung cancer, thyroid cancer, pancreatic cancer, prostate cancer, renal cancer and cancers of the digestive tract. Another class of cancer antigens is oncofetal proteins of nonenzymatic function. These antigens are found in a variety of neoplasms, and are often referred to as “tumor-associated antigens.” Carcinoembryonic antigen (CEA), and α-fetoprotein (AFP) are two examples of such cancer antigens. AFP levels rise in patients with hepatocellular carcinoma: 69% of patients with liver cancer express high levels of AFP in their serum. CEA is a serum glycoprotein of 200 kDa found in adenocarcinoma of colon, as well as cancers of the lung and genitourinary tract. Yet another class of cancer antigens is those antigens unique to a particular tumor, referred to sometimes as “tumor specific antigens,” such as heat shock proteins (e.g., hsp70 or hsp90 proteins) from a particular type of tumor. Other targets include the MICA/B ligands of NKG2D. These molecules are expressed on many types of tumors, but not normally on healthy cells.

Additional specific examples of cancer antigens include epithelial cell adhesion molecule (Ep-CAM/TACSTD1), mesothelin, tumor-associated glycoprotein 72 (TAG-72), gp100, Melan-A, MART-1, KDR, RCAS1, MDA7, cancer-associated viral vaccines (e.g., human papillomavirus antigens), prostate specific antigen (PSA, PSMA), RAGE (renal antigen), CAMEL (CTL-recognized antigen on melanoma), CT antigens (such as MAGE-B5, -B6, -C2, -C3, and D; Mage-12; CT10; NY-ESO-1, SSX-2, GAGE, BAGE, MAGE, and SAGE), mucin antigens (e.g., MUC1, mucin-CA125, etc.), cancer-associated ganglioside antigens, tyrosinase, gp75, C-myc, Mart1, MelanA, MUM-1, MUM-2, MUM-3, HLA-B7, Ep-CAM, tumor-derived heat shock proteins, and the like (see also, e.g., Acres et al., Curr Opin Mol Ther 2004 February, 6:40-7; Taylor-Papadimitriou et al., Biochim Biophys Acta. 1999 Oct. 8; 1455(2-3):301-13; Emens et al., Cancer Biol Ther. 2003 July-August; 2(4 Suppl 1):S161-8; and Ohshima et al., Int J Cancer. 2001 Jul. 1; 93(1):91-6). Other exemplary cancer antigen targets include CA 195 tumor-associated antigen-like antigen (see, e.g., U.S. Pat. No. 5,324,822) and female urine squamous cell carcinoma-like antigens (see, e.g., U.S. Pat. No. 5,306,811), and the breast cell cancer antigens described in U.S. Pat. No. 4,960,716.

The variable domain according to the invention may target protein antigens, carbohydrate antigens, or glycosylated proteins. For example, the variable domain can target glycosylation groups of antigens that are preferentially produced by transformed (neoplastic or cancerous) cells, infected cells, and the like (cells associated with other immune system-related disorders). In one aspect, the antigen is a tumor-associated antigen. In an exemplary aspect, the antigen is O-acetylated-GD2 or glypican-3. In another particular aspect, the antigen is one of the Thomsen-Friedenreich (TF) antigens (TFAs).

The variable domain according to the invention can also exhibit specificity for a cancer-associated protein. Such proteins can include any protein associated with cancer progression. Examples of such proteins include angiogenesis factors associated with tumor growth, such as vascular endothelial growth factors (VEGFs), fibroblast growth factors (FGFs), tissue factor (TF), epidermal growth factors (EGFs), and receptors thereof; factors associated with tumor invasiveness; and other receptors associated with cancer progression (e.g., one of the HER1-HER4 receptors).

Alternatively the variable domain according to the invention can be specific for a virus, a bacteria or parasite associated target. For example, the variable domain may be specific for a virus-associated target such as an HIV protein (e.g., gp120 or gp41), CMV or other viruses, such as hepatitis C virus (HCV).

The variable domain according to the invention may also target albumin or FcRn to increase the half-life of the antigen binding formats of the invention in the systemic circulation.

The variable domain according to the invention may alternatively target a hapten, and more particularly low molecular weight hapten, and more preferably a radiolabeled low molecular weight hapten. Molecular weight haptens according to the invention may be selected from the group consisting of methotrexate, histamine succinyl glycine, DTPA (diethylene triaminepentaacetic acid); DOTA (1,4,7,10-tetraazacyclododecane-N,N′,N″,N′″-tetraacetic acid); and derivatives thereof (see, for example, U.S. Pat. Nos. 4,885,363; 5,087,440; 5,155,215; 5,188,816; 5,219,553; 5,262,532; and 5,358,704; and D. Meyer et al., Invest. Radiol. 1990, 25: S53-55). In particular embodiment, the hapten is labeled with a radionuclide. For example, useful diagnostic radionuclides include, but are not limited to, ¹¹⁰In, ¹⁷⁷Lu, ¹⁸F, ⁵²Fe, ⁶²Cu, ⁶⁴Cu, ⁶⁷Cu, ⁶⁷Ga, ⁶⁸Ga, ⁸⁹Zr, ⁹⁴Tc, ¹⁵⁰Re, ¹⁸⁸Re, or other gamma-, beta-, or positron-emitters. Particularly useful therapeutic radionuclides include, but are not limited to ¹¹¹In, ¹⁷⁷Lu, ²¹²Bi, ²¹³Bi, ²¹¹At, ⁶²Cu, ⁶⁴Cu, ⁶⁷Cu, ⁹⁰Y, ¹²⁵I, ¹³¹I, ³²P, ³³P, ⁴⁷Sc, ¹¹¹Ag, ⁶⁷Ga, ¹⁴²Pr, ¹⁵³Sm, ¹⁶¹Tb, ¹⁶⁶Dy, ¹⁶⁶Ho, ¹⁸⁶Re, ¹⁸⁸Re, ¹⁸⁹Re, ²¹²Pb, ²²³Ra, ²²⁵Ac, ⁵⁹Fe, ⁷⁵Se, ⁷⁷As, ⁸⁹Sr, ⁹⁹Mo, ¹⁰⁵Rh, ¹⁰⁹Pd, ¹⁴³Pr, ¹⁴⁹Pm, ¹⁶⁹Er, ¹⁹⁴Ir, ¹⁹⁸Au, ¹⁹⁹Au, and ²¹¹Pb.

The constant domains and variable domains according to the invention can readily be prepared by an ordinarily skilled artisan using routine experimentation.

For example, the constant domains and variable domains according to the invention may be from monoclonal antibodies. Monoclonal antibodies directed against antigens of interest can be produced by an animal (including, but not limited to, human, mouse, camelid, rat, rabbit, hamster, goat, horse, chicken, or turkey), chemically synthesized, or recombinantly expressed. For example, monoclonal antibodies can be prepared and isolated using any technique that provides for the production of antibody molecules by continuous cell lines in culture. Techniques for production and isolation include but are not limited to the hybridoma technique originally described by Kohler and Milstein (1975); the human B-cell hybridoma technique (Cote et al., 1983); and the EBV-hybridoma technique (Cole et al. 1985). Other known methods of producing transformed B cell lines that produce monoclonal antibodies may also be used. Monoclonal antibodies of the present invention may be produced by recombinant DNA techniques, for example, produced by phage display or by combinatorial methods. See, for example, U.S. Pat. No. 5,223,409; WO 92/18619; WO 91/17271; WO 92/20791; WO 92/15679; WO 93/01288; WO 92/01047; WO 92/09690; or WO 90/02809. Monoclonal antibodies of the present invention can be purified by any method known in the art for purification of an immunoglobulin molecule, for example, by chromatography (e.g., ion exchange, affinity, and sizing column chromatography), centrifugation, differential solubility, or by any other standard technique for the purification of proteins. In addition, the antibodies can be fused to heterologous polypeptide sequences described herein or otherwise known in the art, to facilitate purification. Finally, the genes encoding the constant domain or variable domain according to the invention can be recovered from the DNA of relevant hybridomas or phages. In a particular embodiment, monoclonal antibodies are full-human antibodies or humanized antibodies.

sdAbs are usually generated by PCR cloning of the V-domain repertoire from blood, lymph node, or spleen cDNA obtained from immunized animals into a phage display vector, such as pHEN2. Antigen-specific sdAbs are commonly selected by panning phage libraries on immobilized antigen, e.g., antigen coated onto the plastic surface of a test tube, biotinylated antigens immobilized on streptavidin beads, or membrane proteins expressed on the surface of cells. However, such sdAbs often show lower affinities for their antigen than sdAbs derived from animals that have received several immunizations. The high affinity of sdAbs from immune libraries is attributed to the natural selection of variant sdAbs during clonal expansion of B-cells in the lymphoid organs of immunized animals. The affinity of sdAbs from non-immune libraries can often be improved by mimicking this strategy in vitro, i.e., by site directed mutagenesis of the CDR regions and further rounds of panning on immobilized antigen under conditions of increased stringency (higher temperature, high or low salt concentration, high or low pH, and low antigen concentrations). sdAbs derived from camelid are readily expressed in and purified from the E. coli periplasm at much higher levels than the corresponding domains of conventional antibodies. sdAbs generally display high solubility and stability and can also be readily produced in yeast, plant, and mammalian cells. For example, the “Hamers patents” describe methods and techniques for generating VHH against any desired target (see for example U.S. Pat. No. 5,800,988; U.S. Pat. No. 5,874,541 and U.S. Pat. No. 6,015,695). The “Hamers patents” more particularly describe production of sdAbs in bacterial hosts such as E. coli (see for example U.S. Pat. No. 6,765,087) and in lower eukaryotic hosts such as moulds (for example Aspergillus or Trichoderma) or in yeast (for example Saccharomyces, Kluyveromyces, Hansenula or Pichia) (see for example U.S. Pat. No. 6,838,254). In a specific antibody, the sdAbs of the invention may be further humanized.

According to the invention, the CH1 and CL constant domains of the fusion proteins are fused directly at their N-terminal ends to the C-terminal end of a variable domain of an antibody.

As used herein, the term “directly” means that the (first or last) amino acid at the terminal end (N or C-terminal end) of the constant domain is fused to the (first or last) amino acid at the terminal end (N or C-terminal end) of the variable domain.

In other words, in this embodiment, the first amino acid of the N-terminal end of said CH1 or CL constant domain is directly linked by a covalent bond to the last amino acid of the C-terminal end of said variable domain of an antibody.

According to the invention, the CH1 constant domain of the first fusion protein is fused by its C-terminal end to the N-terminal end of a variable domain of an antibody either directly or via a spacer.

As used herein, the term “spacer” refers to a sequence of at least one amino acid that links the constant domain with the variable domain of the invention. Such a spacer may be useful to prevent steric hindrances. Typically, said spacer is an amino acid sequence selected from the group consisting of AAA (SEQ ID NO:29) and DKT (SEQ ID NO:30). Preferably, said spacer is the sequence DKT naturally present at the C-terminal end of the human CH1 domain of antibodies.

Preferably, the antigen binding format according to the invention consists of:

-   -   a first fusion protein consisting of a CH1 domain of an antibody         fused directly by its N-terminal end to the C-terminal end of a         variable domain of an antibody, and fused via a spacer by its         C-terminal end to the N-terminal end of a variable domain of an         antibody, said spacer being preferably AAA or DKT and,     -   a second fusion protein consisting of a CL domain of an antibody         fused directly by its N-terminal end to the C-terminal end of a         variable domain of an antibody.

According to the invention, the antigen binding formats of the invention have 3 variable domains and can therefore be mono, bi, or tri specific toward antigens of interest. Accordingly, every variable domains of the antigen binding format according to the invention has the ability to bind to an antigen by itself. The binding to the antigen is not as the same as classically observed for an antibody binding to an antigen (the entity responsible for the binding to the antigen is the complex formed by the VL and CH variable domains) but approaches to the same as observed for camelid mammals: a variable domain (VH, VL or VHH) can bind to an antigen by itself.

In a particular embodiment, the present invention relates to an antigen-binding format consisting of:

-   -   a first fusion protein wherein the CH1 constant domain of an         antibody is fused i) by its N-terminal end to the C-terminal end         of a variable domain of an antibody and ii) by its C-terminal         end to the N-terminal end of a variable domain of an antibody         and,     -   a second fusion protein wherein the CL constant domain of an         antibody is fused by its N-terminal end to the C-terminal end of         a variable domain of an antibody.

with the exception of an antigen-binding format consisting of:

-   -   a first fusion protein wherein the CH1 constant domain of an         antibody is fused i) by its N-terminal end to the C-terminal end         of a VH variable domain of an antibody and ii) by its C-terminal         end to the N-terminal end of a variable domain of an antibody         and,     -   a second fusion protein wherein the CL constant domain of an         antibody is fused by its N-terminal end to the C-terminal end of         a VL variable domain of an antibody     -   wherein the VH variable domain of the first fusion protein and         VL variable domain of the second fusion protein do not         constitute a unique antigen-binding site (i.e. the assembly of 2         fusion proteins does not constitute a fragment antigen-binding         (Fab fragment)).

In a particular embodiment, the present invention relates to an antigen-binding format consisting of:

-   -   a first fusion protein wherein the CH1 constant domain of an         antibody is fused i) by its N-terminal end to the C-terminal end         of a variable domain of an antibody and ii) by its C-terminal         end to the N-terminal end of a variable domain of an antibody         and,     -   a second fusion protein wherein the CL constant domain of an         antibody is fused by its N-terminal end to the C-terminal end of         a variable domain of an antibody.

with the exception of an antigen-binding format consisting of:

-   -   a first fusion protein wherein the CH1 constant domain of an         antibody is fused i) by its N-terminal end to the C-terminal end         of a VH variable domain of an antibody and ii) by its C-terminal         end to the N-terminal end of a variable domain of an antibody         and,     -   a second fusion protein wherein the CL constant domain of an         antibody is fused by its N-terminal end to the C-terminal end of         a VL variable domain of an antibody

In some embodiments, the antigen binding format of the invention may be monospecific when all variable domains are directed against the same antigen. Moreover, the antigen binding format of the invention may be bispecific, when combination of variable domains makes them directed against two particular antigens (e.g. CEA and CD16). According to this embodiment, said antigen binding format is bivalent; i.e. two of the three variable domains are directed against the same antigen (e.g. CEA or CD16). Furthermore, the antigen binding format of the invention may be trispecific, when combination of variable domains makes them directed against three particular antigens (e.g. CEA, CD3 and CD16 or CEA, CD16, human albumin or CEA, CD3, human albumin).

In a particular embodiment, the antigen binding format of the invention is bispecific wherein two variable domains are specific for a cancer antigen (e.g. CEA) and the last variable domain is specific for an immune cell regulatory molecule (e.g. CD16).

In a particular embodiment, the antigen binding format of the invention is trispecific wherein a first variable domain is specific for a cancer antigen (e.g. CEA or any cancer antigen), a second variable domain is specific for a first immune cell regulatory molecule (e.g. CD16), and a third variable domain is specific for a second immune cell regulatory molecule (e.g. CD3). More particularly, the invention relates to an antigen binding format wherein a first variable domain is specific for a cancer antigen, a second variable domain is specific for a natural killer cell molecule (e.g. CD16), and a third variable domain is specific for a T cell molecule (e.g. CD3). provides the advantage to kill tumor cells more potently by providing both NK cells and T cells retargeting. Said binding antigen format also contributes to the stimulation of the adaptive immune system, because tumor killing T-lymphocytes could potentially be generated, and vaccination could be established (ie, the provision of long-term immune response and memory cells that could rapidly generate a new and efficient response in the case of metastasis development).

In a particular embodiment, the antigen binding format of the invention consists of:

-   -   a first fusion protein consisting of a CH1 domain fused directly         by its N-terminal end to a single domain antibody specific for         CD16 and fused via a spacer by its C-terminal end to a single         domain antibody specific for carcinoembryonic antigen (CEA)         wherein said spacer is AAA or DKT; and     -   a second fusion protein consisting of a CL domain of a kappa (κ)         light chain fused directly by its N-terminal end with a single         domain antibody specific for carcinoembryonic antigen (CEA).

In a particular embodiment, an antigen binding format of the invention is represented by format 514-515 or 1214-1215 in FIG. 1.

In a particular embodiment, the antigen binding format of the invention is trispecific wherein the first variable domain is specific for a cancer antigen (e.g. CEA), the second variable domain is specific for a immune cell regulatory molecule (e.g. CD16), and the third variable domain is specific for albumin. More particularly, the invention relates to an antigen binding format wherein a first variable domain is specific for a cancer antigen, a second variable domain is specific for a natural killer cell molecule (e.g. CD16), and a third variable domain is specific for a albumin. The half life of the antigen binding format in the systemic circulation may be thus increased without affecting its tumor cell killing effects.

Nucleic Acids, Vectors and Recombinant Host Cells of the Invention

A further object of the present invention relates to a nucleic acid molecule encoding for an antigen binding format according to the invention.

As used herein, a sequence “encoding” an expression product, such as a RNA, polypeptide, protein, or enzyme, is a nucleotide sequence that, when expressed, results in the production of that RNA, polypeptide, protein, or enzyme, i.e., the nucleotide sequence encodes an amino acid sequence for that polypeptide, protein or enzyme. A coding sequence for a protein may include a start codon (usually ATG) and a stop codon.

These nucleic acid molecules can be obtained by conventional methods well known to those skilled in the art.

Typically, said nucleic acid is a DNA or RNA molecule, which may be included in a suitable vector, such as a plasmid, cosmid, episome, artificial chromosome, phage or viral vector.

So, a further object of the present invention relates to a vector and an expression cassette in which a nucleic acid molecule encoding for an antigen binding format of the invention is associated with suitable elements for controlling transcription (in particular promoter, enhancer and, optionally, terminator) and, optionally translation, and also the recombinant vectors into which a nucleic acid molecule in accordance with the invention is inserted. These recombinant vectors may, for example, be cloning vectors, or expression vectors.

As used herein, the terms “vector”, “cloning vector” and “expression vector” mean the vehicle by which a DNA or RNA sequence (e.g. a foreign gene) can be introduced into a host cell, so as to transform the host and promote expression (e.g. transcription and translation) of the introduced sequence.

According to the invention, the vector is a bicistronic vector that includes two nucleic acid molecules, each one encoding for a fusion protein of the antigen binding format.

Any expression vector for animal cell can be used. Examples of suitable vectors include pAGE107 (Miyaji H et al. 1990), pAGE103 (Mizukami T et al. 1987), pHSG274 (Brady G et al. 1984), pKCR (O'Hare K et al. 1981), pSG1 beta d2-4-(Miyaji H et al. 1990) and the like.

Other examples of plasmids include replicating plasmids comprising an origin of replication, or integrative plasmids, such as for instance pUC, pcDNA, pBR, and the like.

Other examples of viral vectors include adenoviral, retroviral, herpes virus and AAV vectors. Such recombinant viruses may be produced by techniques known in the art, such as by transfecting packaging cells or by transient transfection with helper plasmids or viruses. Typical examples of virus packaging cells include PA317 cells, PsiCRIP cells, GPenv+ cells, 293 cells, etc. Detailed protocols for producing such replication-defective recombinant viruses may be found for instance in WO 95/14785, WO 96/22378, U.S. Pat. No. 5,882,877, U.S. Pat. No. 6,013,516, U.S. Pat. No. 4,861,719, U.S. Pat. No. 5,278,056 and WO 94/19478.

Examples of promoters and enhancers used in the expression vector for animal cell include early promoter and enhancer of SV40 (Mizukami T. et al. 1987), LTR promoter and enhancer of Moloney mouse leukemia virus (Kuwana Y et al. 1987), promoter (Mason J O et al. 1985) and enhancer (Gillies S D et al. 1983) of immunoglobulin H chain and the like.

The invention also includes gene delivery systems comprising a nucleic acid molecule of the invention, which can be used in gene therapy in vivo or ex vivo. This includes for instance viral transfer vectors such as those derived from retrovirus, adenovirus, adeno associated virus, lentivirus, which are conventionally used in gene therapy. This also includes gene delivery systems comprising a nucleic acid molecule of the invention and a non-viral gene delivery vehicle. Examples of non viral gene delivery vehicles include liposomes and polymers such as polyethylenimines, cyclodextrins, histidine/lysine (HK) polymers, etc.

A subject of the present invention is also a prokaryotic or eukaryotic host cell genetically transformed with at least one nucleic acid molecule or vector according to the invention (preferably a bicistronic vector as above described).

The term “transformation” means the introduction of a “foreign” (i.e. extrinsic or extracellular) gene, DNA or RNA sequence to a host cell, so that the host cell will express the introduced gene or sequence to produce a desired substance, typically a protein or enzyme coded by the introduced gene or sequence. A host cell that receives and expresses introduced DNA or RNA has been “transformed”.

In a particular embodiment, for expressing and producing antigen binding formats of the invention, prokaryotic cells, in particular E. coli cells, will be chosen. Actually, according to the invention, it is not mandatory to produce the antigen binding format of the invention in a eukaryotic context that will favour post-translational modifications (e.g. glycosylation). Furthermore, prokaryotic cells have the advantages to produce protein in large amounts. If a eukaryotic context is needed, yeasts (e.g. saccharomyces strains) may be particularly suitable since they allow production of large amounts of proteins. Otherwise, typical eukaryotic cell lines such as CHO, BHK-21, COS-7, C127, PER.C6, YB2/0 or HEK293 could be used, for their ability to process to the right post-translational modifications of the antigen binding format of the invention.

Accordingly, a further aspect of the invention relates to a host cell comprising a nucleic acid molecule encoding for an antigen binding format according to the invention or a vector according to the invention.

The construction of expression vectors in accordance with the invention, and the transformation of the host cells can be carried out using conventional molecular biology techniques. The antigen binding formats of the invention, can, for example, be obtained by culturing genetically transformed cells in accordance with the invention and recovering the antigen binding format expressed by said cell, from the culture. They may then, if necessary, be purified by conventional procedures, known in themselves to those skilled in the art, for example by fractional precipitation, in particular ammonium sulfate precipitation, electrophoresis, gel filtration, affinity chromatography, etc. . . . In particular, conventional methods for preparing and purifying recombinant proteins may be used for producing the proteins in accordance with the invention.

A further aspect of the invention relates to a method for producing an antigen binding format of the invention comprising the step consisting of: (i) culturing a transformed host cell according to the invention under conditions suitable to allow expression of said antigen binding format; and (ii) recovering the expressed antigen binding format.

Therapeutic Methods and Uses of the Invention

The present invention provides methods and compositions (such as pharmaceutical compositions) for treating cancer or infectious diseases. Antigen binding formats of the invention are indeed particularly suitable for the treatment of diseases such as cancer or infectious diseases.

Therefore, a further object of the invention relates to an antigen binding format of the invention for use as a medicament.

More particularly, an aspect of the invention relates to an antigen binding format of the invention for use in the treatment of cancer or infectious diseases.

In the context of the invention, the term “treating” or “treatment”, as used herein, means reversing, alleviating, inhibiting the progress of, or preventing the disorder or condition to which such term applies, or one or more symptoms of such disorder or condition.

As used herein, the term “infectious disease” is intended to encompass any disease which results from an infection mediated by a virus, a bacteria or a parasite. Therefore the term includes but is not limited to infection with virus such as human immunodeficiency virus, Hepatitis B virus, hepatitis C virus, with parasites such as Plasmodium Falciparum (causative agent for Malaria), or with bacteria such as mycobacterium tuberculosis.

As used herein, the term “cancer” is intended to encompass primary and metastatic solid tumors, including carcinomas of breast, colon, rectum, lung, oropharynx, hypopharynx, esophagus, stomach, pancreas, liver, gallbladder and bile ducts, small intestine, kidney, bladder, urothelium, female genital tract, (including cervix, uterus, and ovaries as well as choriocarcinoma and gestational trophoblastic disease), male genital tract (including prostate, seminal vesicles, testes and germ cell tumors), endocrine glands (including the thyroid, adrenal, and pituitary glands), and skin, as well as hemangiomas, melanomas, sarcomas (including those arising from bone and soft tissues as well as Kaposi's sarcoma) and tumors of the brain, nerves, eyes, such as astrocytomas, gliomas, glioblastomas, retinoblastomas, neuromas, neuroblastomas, Schwannomas, and meningiomas. The term cancer also relates to tumors arising from hematopoietic malignancies such as leukemias as well both Hodgkin's and non-Hodgkin's lymphomas.

A further aspect of the invention relates to a method for treating cancer or an infectious disease, comprising administering to a subject in need thereof an amount of antigen binding format according to the invention.

As used herein, the term “subject” denotes a mammal, such as a rodent, a feline, a canine, and a primate. Preferably, a subject according to the invention is a human.

The antigen binding format of the invention may be administered in the form of a pharmaceutical composition, as defined below.

Preferably, the antigen binding formats of the invention are administered in a therapeutically effective amount.

The term “therapeutically effective amount” means a sufficient amount of the active ingredients of the invention to treat cancer or infectious disease at a reasonable benefit/risk ratio applicable to any medical treatment.

It will be understood that the total daily usage of the antigen binding formats of the invention will be decided by the attending physician within the scope of sound medical judgment. The specific therapeutically effective dose level for any particular subject will depend upon a variety of factors including the disorder being treated and the severity of the disorder; activity of the specific compound employed; the specific composition employed, the age, body weight, general health, sex and diet of the subject; the time of administration, route of administration, and rate of excretion of the specific antigen binding formats employed; the duration of the treatment; drugs used in combination or coincidental with the specific antigen binding formats employed; and like factors well known in the medical arts. For example, it is well within the skill of the art to start doses of the antigen binding formats at levels lower than those required to achieve the desired therapeutic effect and to gradually increase the dosage until the desired effect is achieved.

An approach to cancer therapy and diagnosis may also involve the use of a bispecific antigen binding format according to the invention having at least one arm that specifically binds a cancer antigen and at least one other arm that specifically binds a low molecular weight hapten. In this methodology, the antigen binding format of the invention is administered and allowed to target the cancer antigen and therefore the tumour. Some time later, a radiolabeled low molecular weight hapten is given, which being recognized by the second specificity of the antigen binding format, also localizes to the tumour.

In another particular embodiment, the antigen binding format according to the invention may act as a ligand for a cell receptor or channel. Therefore the antigen binding format according to the invention may represent an agonist, a partial agonist or an antagonist for a receptor.

Diagnostic Methods and Uses of the Invention

Antigen binding formats of the invention may also be particularly suitable for diagnosing or monitoring a disease. Said disease may be any disease and may be selected for example from the group consisting of cancers and infectious diseases.

A further aspect of the invention relates to the use of an antigen binding format of the invention for diagnosing or monitoring a disease that may be selected from the group consisting of cancers and infectious diseases.

In a particular embodiment, antigen binding formats of the invention may be labelled with a detectable molecule or substance, such as a fluorescent molecule, a radioactive molecule or any others labels known in the art. Labels are known in the art to generally provide (either directly or indirectly) a signal.

As used herein, the term “labelled”, with regard to the antibody, is intended to encompass direct labelling of the antibody by coupling (i.e., physically linking) a detectable substance, such as a radioactive agent or a fluorophore (e.g. fluorescein isothiocyanate (FITC) or phycoerythrin (PE) or indocyanine (Cy5)) to the antibody, as well as indirect labelling of the antibody by reactivity with a detectable substance.

An antigen binding format of the invention may be labelled with a radioactive molecule by any method known to the art. For example radioactive molecules include but are not limited to radioactive atoms for scintigraphic studies such as I123, I124, In111, Re186, Re188. Antigen binding formats of the invention may also be labelled with a spin label for nuclear magnetic resonance (NMR) imaging (also known as magnetic resonance imaging, mri), such as iodine-123, iodine-131, indium-I11, fluorine-19, carbon-13, nitrogen-15, oxygen-17, gadolinium, manganese or iron.

A “biological sample” encompasses a variety of sample types obtained from a subject and can be used in a diagnostic or monitoring assay. Biological samples include but are not limited to blood and other liquid samples of biological origin, solid tissue samples such as a biopsy specimen or tissue cultures or cells derived therefrom, and the progeny thereof. For example, biological samples include cells obtained from a tissue sample collected from an individual suspected of having a cancer disease. Therefore, biological samples encompass clinical samples, cells in culture, cell supernatants, cell lysates, serum, plasma, biological fluid, and tissue samples.

Antigen binding formats of the invention may be useful for staging of cancer diseases (e.g., in radioimaging).

Pharmaceutical Compositions and Kits of the Invention

The invention also relates to pharmaceutical compositions comprising antigen binding formats of the invention.

Therefore, antigen binding formats of the invention may be combined with pharmaceutically acceptable excipients, and optionally sustained-release matrices, such as biodegradable polymers, to form therapeutic compositions.

“Pharmaceutically” or “pharmaceutically acceptable” refers to molecular entities and compositions that do not produce any adverse, allergic or other untoward reaction when administered to a mammal, especially a human, as appropriate. A pharmaceutically acceptable carrier or excipient refers to a non-toxic solid, semisolid or liquid filler, diluent, encapsulating material or formulation auxiliary of any type.

The form of the pharmaceutical compositions, the route of administration, the dosage and the regimen naturally depend upon the condition to be treated, the severity of the illness, the age, weight, and sex of the patient, etc.

The pharmaceutical compositions of the invention can be formulated for a topical, oral, parenteral, intranasal, intravenous, intramuscular, subcutaneous or intraocular administration and the like.

Preferably, the pharmaceutical compositions contain vehicles which are pharmaceutically acceptable for a formulation capable of being injected. These may be in particular isotonic, sterile, saline solutions (monosodium or disodium phosphate, sodium, potassium, calcium or magnesium chloride and the like or mixtures of such salts), or dry, especially freeze-dried compositions which upon addition, depending on the case, of sterilized water or physiological saline, permit the constitution of injectable solutions.

The doses used for the administration can be adapted as a function of various parameters, and in particular as a function of the mode of administration used, of the relevant pathology, or alternatively of the desired duration of treatment.

To prepare pharmaceutical compositions, an effective amount of the antigen binding format may be dissolved or dispersed in a pharmaceutically acceptable carrier or aqueous medium.

The pharmaceutical forms suitable for injectable use include sterile aqueous solutions or dispersions; formulations including sesame oil, peanut oil or aqueous propylene glycol; and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersions. In all cases, the form must be sterile and must be fluid to the extent that easy syringability exists. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms, such as bacteria and fungi.

Solutions of the active compounds as free base or pharmacologically acceptable salts can be prepared in water suitably mixed with a surfactant, such as hydroxypropylcellulose. Dispersions can also be prepared in glycerol, liquid polyethylene glycols, and mixtures thereof and in oils. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms.

An antigen binding format of the invention can be formulated into a composition in a neutral or salt form. Pharmaceutically acceptable salts include the acid addition salts (formed with the free amino groups of the protein) and which are formed with inorganic acids such as, for example, hydrochloric or phosphoric acids, or such organic acids as acetic, oxalic, tartaric, mandelic, and the like. Salts formed with the free carboxyl groups can also be derived from inorganic bases such as, for example, sodium, potassium, ammonium, calcium, or ferric hydroxides, and such organic bases as isopropylamine, trimethylamine, histidine, procaine and the like.

The carrier can also be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for example, glycerol, propylene glycol, and liquid polyethylene glycol, and the like), suitable mixtures thereof, and vegetables oils. The proper fluidity can be maintained, for example, by the use of a coating, such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. The prevention of the action of microorganisms can be brought about by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars or sodium chloride. Prolonged absorption of the injectable compositions can be brought about by the use in the compositions of agents delaying absorption, for example, aluminium monostearate and gelatin.

Sterile injectable solutions are prepared by incorporating the required amount of the active compounds in the appropriate solvent with various/several of the other ingredients enumerated above, as required, followed by filtered sterilization. Generally, dispersions are prepared by incorporating the various sterilized active ingredients into a sterile vehicle which contains the basic dispersion medium and the other required ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum-drying and freeze-drying techniques which yield a powder of the active ingredient plus any additional desired ingredient from a previously sterile-filtered solution thereof.

The preparation of more, or highly concentrated solutions for direct injection is also contemplated, where the use of DMSO as solvent is envisioned to result in extremely rapid penetration, delivering high concentrations of the active agents to a small tumor area.

Upon formulation, solutions will be administered in a manner compatible with the dosage formulation and in such amount as is therapeutically effective. The formulations are easily administered in a variety of dosage forms, such as the type of injectable solutions described above, but drug release capsules and the like can also be employed.

For parenteral administration in an aqueous solution, for example, the solution should be suitably buffered if necessary and the liquid diluent first rendered isotonic with sufficient saline or glucose. These particular aqueous solutions are especially suitable for intravenous, intramuscular, subcutaneous and intraperitoneal administration. In this connection, sterile aqueous media which can be employed will be known to those of skill in the art in light of the present disclosure. For example, one dosage could be dissolved in 1 ml of isotonic NaCl solution and either added to 1000 ml of hypodermoclysis fluid or injected at the proposed site of infusion, (see for example, “Remington's Pharmaceutical Sciences” 15th Edition, pages 1035-1038 and 1570-1580). Some variation in dosage will necessarily occur depending on the condition of the subject being treated. The person responsible for administration will, in any event, determine the appropriate dose for the individual subject.

The antigen binding formats of the invention may be formulated within a therapeutic mixture to comprise about 0.0001 to 1.0 milligrams, or about 0.001 to 1.0 milligrams, or about 0.01 to 1.0 milligrams, or about 0.1 to 1.0 milligrams or even about 10 milligrams per dose or so. Multiple doses can also be administered.

In addition to the compounds formulated for parenteral administration, such as intravenous or intramuscular injection, other pharmaceutically acceptable forms include, e.g. tablets or other solids for oral administration; time release capsules; and any other form currently used.

In certain embodiments, the use of liposomes and/or nanoparticles is contemplated for the introduction of antigen binding formats into host cells. The formation and use of liposomes and/or nanoparticles are known to those of skill in the art.

Nanocapsules can generally entrap compounds in a stable and reproducible way. To avoid side effects due to intracellular polymeric overloading, such ultrafine particles (sized around 0.1 μm) are generally designed using polymers able to be degraded in vivo. Biodegradable polyalkyl-cyanoacrylate nanoparticles that meet these requirements are contemplated for use in the present invention, and such particles may be easily made.

Liposomes are formed from phospholipids that once dispersed in an aqueous medium spontaneously form multilamellar concentric bilayer vesicles (also termed multilamellar vesicles (MLVs)). MLVs generally have diameters ranging from 25 nm to 4 μm. Sonication of MLVs results in the formation of small unilamellar vesicles (SUVs) with diameters in the range of 200 to 500 Å, containing an aqueous solution in the core. The physical characteristics of liposomes depend on pH, ionic strength and the presence of divalent cations.

The invention also provides kits comprising at least one antigen binding format of the invention. Kits containing antigen binding formats of the invention find use in therapeutic methods or diagnostic assays.

The invention will be further illustrated by the following figures and examples. However, these examples and figures should not be interpreted in any way as limiting the scope of the present invention.

FIGURES

FIG. 1: Representation of various bispecific antibody formats.

FIG. 2: Flow cytometry experiments demonstrating a higher apparent affinity of bivalent (bbsAb) vs. monovalent (bsFab) bispecific antibodies. CEA: MC38-CEA cells CD16: Jurkat-CD16 cells.

FIG. 3: In vitro cytotoxicity assays performed by flow cytometry using human NK cells and bispecific antibodies

EXAMPLE Material & Methods 1/ Construction of the New Formats

p501 (SEQ ID NO:9): Insertion of anti-CEA sdAb 17 gene (Behar, G., Chames, P., Teulon, I., Cornillon, A., Alshoukr, F., Roquet, F., Pugniere, M., Teillaud, J.-L., Gruaz-Guyon, A., Pelegrin, A. and Baty, D Llama single domain antibodies directed against non-conventional epitopes of tumor-associated carcinoembryonic antigen (CEA) absent from non-specific cross-reacting antigen (NCA). FEBS J, 2009, 276, 3881-93) of pHen1-CEA17 (SEQ ID NO:10) into p1 (SEQ ID NO:11) at the C-terminal end of CH1 domain (Not I site):

PCR: 5 ng pHen1-CEA17 (SEQ ID NO:10), 0.5 U Taq Polymerase Deep-vent (New England Biolabs), 10 μM of primer 5′ Not VHH and primer 3′ Not VHH rev, 5 μL Tp 10×, 1 μl MgSO₄ 1 mM, 4 μl dNTP 2.5 mM, H₂O up to 50 μl, 94° C. 3 min, 94° C. 45 sec, 60° C. 45 sec, 72° C. 45 sec×35 cycles, 72° C. 10 min.

Primer 5′ Not VHH Not SEQ ID NO 1: CCACGATTCTGCGGCCGCAGAGGTGCAGCTGGTGGAGTCTGG Primer 3′ Not VHH rev SEQ ID NO 2: TTTTTGTTCTGCGGCCGCTGAGGAGACGGTGACCTGGG

The PCR fragment was purified on 2% agarose gel using NucleoSpin Extract II kit (Macherey-Nagel) and eluted in 50 μL of buffer NE.

Digestion of p1 (SEQ ID NO:11) (5 μg) by Not I (50 U), 30 μL buffer 3 10×, 30 μL BSA 10 mg/ml, H₂O up to 300 μl 1 h at 37° C. followed by dephosphorylation using 10 U of CIP (Biolabs), 30 min at 37° C. CIP was inactivated using 9 μl EDTA 0.5 M 1 h at 65° C., phenol-treated, and precipitated 16 h at −20° C. using 1 volume NaOAc 0.3M and 3 volumes ethanol 96%, followed by centrifugation 10 min at 16 000 g, washing of the pellet using 750 μl ethanol 70%. The dried pellet was resuspended in 20 μl H₂O.

PCR fragment (20 μl) was digested using NotI (100 U) (30 μl buffer 3 10×, 30 μl BSA 10 mg/ml, H₂O up to 300 μl 1 h at 37° C.). After phenol treatment, the digested PCR fragment was precipitated 16 h at −20° C. using 1 volume NaOAc 0.3 M and 3 volumes ethanol 96%, followed by centrifugation 10 min at 16 000 g, washing of the pellet using 750 μl ethanol 70%. The dried pellet was resuspended in 20 μL H₂O.

Ligation: 120 ng of vector p1 (SEQ ID NO:11) and 60 ng of PCR fragment using 10 U of ligase (Biolabs), 1 μl of buffer 10×, H₂O up to 10 μl, 1 h at RT, 10 min at 65° C.

Three μl of the ligation was electroporated into 40 μl of electrocompetent TG1 cell. Cells were resuspended in 1 ml SOC, 1 h at 37° C., shaked at 180 rpm, and plate on LB/ampicillin dishes.

Two 2 sets of colony-PCRs were performed on 48 colonies to check the ligation event.

PCR1: Primer 5′ M13 Reverse SEQ ID NO 3: CAGGAAACAGCTATGAC and Primer 3′ Hind 111 + 40 SEQ ID NO 4: GCTGAAAATCTTCTCTCATCCG PCR2: Primer 5′ Flag SEQ ID NO 5: GCAGGTGATTACAAAGACGATG and Primer 3′ Not VHH rev (SEQ ID NO 2)

(0.25 U Dynazyme II (Finnzyme), 2.5 μL buffer 10×, 10 mM dNTP, H₂O up to 25 μL, 94° C. 3 min, 94° C. 45 sec, 60° C. 45 sec, 72° C. 45 sec×35 cycles, 72° C. 10 min).

Four positive clones were assayed for expression: induction 12 h at 30° C., IPTG 100 μM, loading of cell lysate on SDS-PAGE 15%, and western blot using 9E10-HRP diluted 1/100).

The sequences were checked (Millegen).

p514 (SEQ ID NO:12): Insertion of the NheI/HindIII fragment from p501 (SEQ ID NO:9) into p14 (SEQ ID NO:13):

10 μg of each vector was digested in 10 μl buffer 2 10×, 10 μl of BSA (10 mg/ml) 20 U NheI, 20 U HindIII, H₂O up to 100 μl, 1 h at 37° C. p14 (SEQ ID NO:13) was dephosphorylated and resuspended in TE (see above).

Fragments were gel purified as above using NucleoSpin Extract II (Macherey-Nagel) and eluted using 25 μl H₂O. Fragments were ligated and ligation was electroporated as above.

Colony-PCR was performed using primers 5′ sigpelbfor (SEQ ID NO 6: TACCTATTGCCTACGGCAGCC) and 3′ HindIII+40 (SEQ ID NO 4), 0.25 U Dynazyme II (Finnzyme), 2.5 μl buffer 10×, 4 μl dNTP 2.5 mM, H₂O up to 25 μl, 94° C. 3 min, 94° C. 1 min 30 sec, 60° C. 1 min 30 sec, 72° C. 1 min 30 sec×35 cycles, 72° C. 10 min. Four positive clones were assayed for expression as above, and sequences were checked (Millegen)

p515 (SEQ ID NO:14): Insertion of the NheI/HindIII fragment from p501 (SEQ ID NO:9) into p15 (SEQ ID NO:15):

As for p514

p1201 (SEQ ID NO:16): Mutation from AAA to DKT spacer on p501 (SEQ ID NO:9):

Quikchange on p501 (SEQ ID NO:9) using 125 ng of each primer, 5 μl of buffer 10×, 4 μl dNTP, 2.5 U Pfu Ultra (Stratagene), H₂O up to 50 μl, 95° C. 1 min, 95° C. 30 sec, 55° C. 1 min, 68° C. 7 min, ×18 cycles, add 40 U Dpn I

Primer 5′ 1201 for SEQ ID NO: 7: GTTGAGCCCAAATCTTGTGACAAAACTGAGGTGCAGCTGGTGG Primer 3′ 1201rev SEQ ID NO 14: CCACCAGCTGCACCTCAGTTTTGTCACAAGATTTGGGCTCAAC

Transformation was performed by electroporation into DH5α using 2 μl of Quikchange product.

Clones were tested for expression as above and sequences were checked.

p1214 (SEQ ID NO:17): Insertion of Nhe I/Hind III fragment from p1201 (SEQ ID NO:16) into p14 (SEQ ID NO:13):

Digest 1 μg of p14 (SEQ ID NO:13) and 15 μg of p1201 (SEQ ID NO:16) by NheI 20 U for p14 (SEQ ID NO:8) and 60 U for p1201 (SEQ ID NO:16) and HindIII 20 U for p14 and 60 U for p1201 using buffer 2 1× final H₂O up to 50 μl, 2 h at 37° C., dephosphorylate vector 14 by adding 10 U of CIP, 30 min at 37° C., add 1.5 μl EDTA 0.5M, followed by phenol extraction, ethanol precipitate and resuspend in 20 μl H₂O.

Gel-purify fragment from p1201 (SEQ ID NO:16) using NucleoSpin Extract II.

Ligation using various vector ratios: insert, using 10 μl Buffer 2×, 3 U T4 DNA ligase (Promega), H₂O up to 50 μl, 15 min RT, 15 min at 65° C., ethanol precipitate and resuspend in 4 μl H₂O

Electroporate 40 μl of DH5α using 4 μl of ligation, plate on LB/Ampi 100 μg/ml petri dishes

Clones were tested for expression as above and sequences were checked.

p1215 (SEQ ID NO:18): as for p1214 (SEQ ID NO:17) but using p15 (SEQ ID NO:15):

2/ Production and Purification of Abs 2.1 Production in E. Coli

The E. coli K12 strain DH5α was used for the Ab production. First, a single colony containing the plasmid of interest was inoculated in 50 ml of LB medium supplemented with ampicillin 100 μg/ml and 2% glucose. The bacteria were grown at 30° C. and shaken at 205 rpm overnight. Four hundred ml of LB medium supplemented with ampicillin 100 μg/ml was inoculated with the previous culture to obtain an OD_(600 nm) of 0.1. The bacteria were grown at 30° C. for 2 h 30, then at 20° C. to an OD_(600 nm) of 0.8-1. The production of Abs was induced by addition of 0.1 mM IPTG (Isopropyl-β-D-thiogalactopyranoside) for 60 h at 20° C.

2.2 Extraction of the Soluble Fraction of the Periplasm

Cells were harvested by centrifugation at 1860 g for 30 min at 4° C. The pellet was thoroughly resuspended in 4 ml of cold TES buffer pH 8.0 (0.2 M Tris HCl pH 8, 0.5 mM EDTA, 0.5 M Sucrose) before adding 1.6 mg of freshly made lysosyme solution. The cells were then submitted to an osmotic shock by addition of 8 ml of cold TES buffer and 8 ml of cold water. After an incubation of 30 min on ice, 250 μg of DNAse I (Roche) and 250 μl of 1 M MgCl₂ were added and the mixture was further incubated 30 min at room temperature. The mixture was centrifuged at 1860 g for 1 h at 4° C. After addition of one tablet of a protease inhibitor cocktail, Complete EDTA-free (Roche) into 50 ml of supernatant, the supernatant was dialyzed for 16 h at 4° C. against 50 mM sodium acetate buffer pH 7.0 containing 0.1 M NaCl.

2.3 Purification of Abs Purification by Cobalt Affinity Chromatography

After filtration on 0.2 μm filter (Millipore), the supernatant was loaded on a 2 ml BD Talon™ Metal Affinity column (BD Biosciences Clontech) previously equilibrated in a 50 mM sodium acetate buffer pH 7.0 containing 0.1 M NaCl. The column was washed with 5 volumes of 50 mM sodium acetate buffer pH 7.0 containing 1 M NaCl then with 5 volumes of 50 mM sodium acetate buffer pH 7.0 containing 0.1 M NaCl. Elution was performed by a linear imidazol gradient (0 to 250 mM). The elution profile was followed spectrophotometrically at 280 nm. The purified fractions were analyzed by SDS PAGE 12% stained with Coomassie blue and western blotting using anti cmyc-HRP antibody (1 μg/ml, Santa Cruz Biotechnologies) and anti-flag-HRP antibody (0.5 μg/ml, Sigma).

Purification by Affinity Chromatography on Protein G

The fractions containing Abs were pooled, dialyzed against PBS buffer (137 mM NaCl, 2.7 mM KCl, 1.2 mM Na2HPO4, 1.76 mM KH2PO4 pH 7.4) and loaded onto a 1 ml Hi-Trap Protein G column (Amersham Biosciences). After washing the column with 5 volumes of PBS, the antibodies were eluted with a 0.1 M glycine HCl buffer pH 2.7 and neutralized by addition of 1/10 volume of 1 M Tris-HCl buffer pH 9.0. The elution profile was followed spectrophotometrically at 280 nm. Purification of Abs was followed by SDS PAGE 12% stained with Coomassie blue and western blotting. Fractions of interest were pooled, washed in PBS and concentrated on Vivaspin devices (cut off 5 kDa, Millipore).

Ab concentrations were determined by the colorimetric method of Lowry using the Biorad protein assay kit. Abs were diluted with one volume of glycerol and stored at −20° C.

3/ Flow Cytometry Experiments

Binding of bsAb to CEA was assessed using MC38-CEA cells. Binding of antibodies to CD16A was assessed using Jurkat-CD16A cells. Cells (5×10⁵ cells/well) were distributed in a V-bottom 96 well microplate and incubated with various concentrations of antibodies (0.82 to 200 nM) for 1 h at 4° C. All cell and antibody dilutions were performed in PBS 1% BSA. Bound antibodies were stained by monoclonal mouse anti c-myc antibody 9E10 (4 μg/ml, (Santa Cruz Biotechnology) for CEA binding or mouse anti-flag M2 antibody (1 μg/ml, Sigma) for CD16A binding, followed by F(ab′)2 goat anti-mouse-FITC antibody (7 μg/mL, Beckman Coulter). After several washes with PBS 1% BSA, labelled cells were gently resuspended in 200 μl PBS BSA 1% and analyzed by flow cytometry on a FACS Calibur cytometer (BD Biosciences). The results were analyzed with CellQuest Pro (BD Biosciences) or Flowjo (Treestart Inc.) softwares.

4/ In Vitro Cytotoxicity Assays 4.1 Isolation of PBMCs (Peripheral Blood Mononuclear Cells)

A blood pack (400 ml) from a healthy donor was recovered in the EFS (Etablissement français du sang) Marseille, France. The blood was diluted in half in PBS 1% FCS and distributed in tubes of blood separation (PAA) previously filled with gradient separation (LSM 1077 Lymphocyte, PAA). The tubes were centrifuged 40 min at 400 g at room temperature with no acceleration and no brake. The opaque ring at the interface between plasma and gradient separation containing PBMCs was recovered. The cells were then washed twice in PBS 1% FCS and centrifuged 20 min at 150 g at room temperature. The cells were then counted on Malassez cell and either resuspended in FCS 20% DMSO and frozen in nitrogen or used for further assays.

4.2 NK Cells Purification

The selection of NK (natural killer) cells was made by negative depletion using the NK cell isolation kit (Milteny Biotec) from PBMCs from healthy donors according to manufactor's indications.

One hundred million of previously isolated PBMC were resuspended in 400 μl of cold buffer (PBS 0.5% BSA 2 mM EDTA). The cells were incubated with 100 μl of a cocktail of antibodies: biotin NK cell antibody cocktail, 10 min on ice. After addition of 300 μL of cold buffer, the cells were incubated with 200 μl of magnetic beads: NK cell cocktail microbeads, 15 min on ice. The cells were then washed with 10 ml of buffer and then resuspended in 500 μl of buffer. The cell suspension was loaded onto the MACS LS column placed in a magnetic field of a MAC Separator and washed with 9 ml of buffer. The unlabelled NK cells were collected, counted and resuspended in culture medium RPMI 10% FCS.

4.3 Cytotoxicity Assay by Flow Cytometry

The cytotoxicity assay by flow cytometry quantifies the lysis of CEA positive target cells induced by CD16+ cells such as NK cells from healthy donors under the action of bsAb.

4.4 Labelling of Target Cells with CFSE

Five millions of CEA+ target cells (MC38-CEA) were washed twice in PBS 1% BSA before addition of CFSE (Carboxyfluorescein succinimidyl ester) at a final concentration of 5 μM in 1 ml of PBS 1% BSA for 10 min in water bath at 37° C. The reaction was then stopped by adding an excess of cold PBS 1% BSA. Cells were washed twice in culture medium RPMI 10% FCS.

CFSE labeled target cells (20 000 cells in 100 μL per well) were incubated with various concentrations of antibodies (1000 pM to 0.01 pM). Each point was made in triplicate. NK cells freshly isolated from PBMC were then added at a effector/target ratio of 10/1. The plate was centrifuged at 560 g for 30 s and incubated at 37° C. for 12 h.

Cells were recovered and washed twice in PBS 1% BSA and incubated for 5 min with 100 μL of 2 nM To-pro3. After addition of 100 μL of PBS 1% BSA, the samples were analyzed by flow cytometry (FACS Calibur, BD Biosciences). Target cell lysis was subsequently measured by release of intracellular label by a scintillation counter or spectrophotometry. Dead target cells were identified as CFSE+/To-pro 3+ cells. % lysis=(% Target+NK+Ab−% Target+NK)/(100−% Target+NK)×100.

Results

The modularity of single domain antibodies combined to the use of the human heterodimerization motif constituted by the CH1/Cκ domains allows the efficient generation of multivalent and/or multispecific recombinant antibodies. We have previously demonstrated the possibility to produce active bispecific monovalent constructs named bsAb (see FIG. 1 and WO/2006/064136) allowing the efficient retargeting and activation of effector cells such as human NK cells and macrophages toward tumor cells, leading to their lysis.

In these constructs, the sdAbs were linked to the N-terminal extremities of CH1 and Cκ domains by their C-terminal extremities. In this work, we wanted to establish the possibility to link the N-terminal end of the sdAb to the C-terminus of the CH1 domain to create multivalent bispecific molecules. Several molecules corresponding to the addition of one anti-CEA domain to the original bsAb format were thus constructed. The N-terminus of sdAbs is located at the tip of the domain, i.e. close to the antigen binding interface. To avoid possible steric clashes, the effect of the addition of small spacers (3 residues, AAA or DKT) was investigated. A representation of these various new formats is shown in FIG. 1.

All these molecules were produced in the periplasm of E. coli to allow a proper disulfide bond formation within each Ig domain and purified after periplasm extraction using a common two-steps procedure, i.e. metal affinity chromatography followed by protein G purification.

Two of the new molecules, i.e. 1214 (SEQ ID NO:25 and SEQ ID NO:26) and 1215 (SEQ ID NO:27 and SEQ ID NO:28) were compared with their monovalent parent molecules (14 and 15) chosen to demonstrate an avidity effect due to the addition of an extra anti-CEA domain, using flow cytometry on CEA+ target cells.

FIG. 2 clearly shows that bivalent constructs 1214 and 1215 yielded higher signals than their parent molecules, especially at low concentration. Altogether, these results demonstrate that single domain added at the C-terminus of CH1 can access and efficiently bind their antigen displayed at the cell surface.

The ability of these new molecules to retarget effector cells toward CEA+ target cells was demonstrated using a flow cytometry based in vitro cytotoxicity assay. CEA+ target cells were fluorescently labelled using CFSE and mixed to human NK cells at an effector: target ratio of 10:1 in the presence of various concentration of monovalent (14 and 15) or bivalent (1214 and 1215) bispecific molecules. As shown in FIG. 3, all molecules displayed a similar activity in this assay with EC₅₀ values in the pM range.

REFERENCES

Throughout this application, various references describe the state of the art to which this invention pertains. The disclosures of these references are hereby incorporated by reference into the present disclosure. 

The invention claimed is:
 1. A nucleic acid molecule encoding for an antigen binding format comprising: a first fusion protein wherein a CH1 constant domain of an antibody is fused i) by its N-terminal end to a C-terminal end of a first single domain antibody and ii) by its C-terminal end to an N-terminal end of a second single domain antibody, wherein the C-terminal end of the CH1 constant domain includes DKT which is fused directly to the N-terminal end of the second single domain antibody, and a second fusion protein wherein a CL constant domain of an antibody is fused by its N-terminal end to a C-terminal end of a third single domain antibody, wherein said first, second and third single domain antibody may be the same or different, and wherein said CH1 constant domain and said CL constant domain are linked via a disulfide bond.
 2. A vector comprising a nucleic acid molecule encoding for an antigen binding format comprising: a first fusion protein wherein a CH1 constant domain of an antibody is fused i) by its N-terminal end to a C-terminal end of a first single domain antibody and ii) by its C-terminal end to an N-terminal end of a second single domain antibody, wherein the C-terminal end of the CH1 constant domain includes DKT which is fused directly to the N-terminal end of the second single domain antibody, and a second fusion protein wherein a CL constant domain of an antibody is fused by its N-terminal end to a C-terminal end of a third single domain antibody, wherein said first, second and third single domain antibody may be the same or different, and wherein said CH1 constant domain and said CL constant domain are linked via a disulfide bond.
 3. A prokaryotic or eukaryotic host cell genetically transformed with at least one nucleic acid molecule encoding for an antigen binding format comprising: a first fusion protein wherein a CH1 constant domain of an antibody is fused i) by its N-terminal end to a C-terminal end of a first single domain antibody and ii) by its C-terminal end to an N-terminal end of a second single domain antibody, wherein the C-terminal end of the CH1 constant domain includes DKT which is fused directly to the N-terminal end of the second single domain antibody, and a second fusion protein wherein a CL constant domain of an antibody is fused by its N-terminal end to a C-terminal end of a third single domain antibody, wherein said first, second and third single domain antibody may be the same or different, and wherein said CH1 constant domain and said CL constant domain are linked via a disulfide bond.
 4. The prokaryotic or eukaryotic host cell of claim 3, wherein said at least one nucleic acid molecule is present in a vector. 